1. Field of the Invention
The present invention relates to an apparatus and a method for cutting and heat sealing a plastic film and, more particularly to a relatively inexpensive and simple apparatus and method which can be used in a highly efficient and continuous manner to cut and heat seal a continuous strip of plastic film to produce, for example, plastic bags.
2. Discussion of the Prior Art
Many different techniques have been employed in the prior art to cut and heat seal a plastic film, particularly on a continuous processing basis. Typically, a heated wire is used to cut and heat seal the film, the wire being brought into contact with the film and then separated therefrom. The mechanism employed in the prior art for moving the heated wire tends to be complex and bulky. In one known technique, for example, illustrated in U.S. Pat. No. 3,054,441, the heated wire is contained on an end of a vane which rotates to first position the wire in contact with a moving plastic film and to thereafter remove the wire from the film. While providing a good cutting and heat sealing operation, the equipment required is complex, bulky and expensive. A considerable amount of energy is also consumed just in rotating the vane. The cutting and heat sealing occurs over a very limited arc of travel, or dwell angle, of the vane which does not provide much flexibility in control of the position at which heat sealing occurs. In addition, a mechanically strong cutting and heat sealing wire is required because of the velocity of rotation of the vane. The wire therefore has a large cross-section and requires substantial amounts of energy for operation. The speed of cutting and heat sealing is also limited by the speed with which the vane may be safely rotated.
Another known technique for moving the heat sealing wire in and out of contact with a plastic film is through a reciprocation mechanism such as that illustrated in U.S. Pat. No. 3,574,039. Again, the difficulty with this type of apparatus is that it is complex, bulky and expensive to operate as considerable amounts of energy are required just to reciprocate the heated wire. In addition, the heated wire is usually in the form of a plate or bar which again consumes a considerable amount of energy in use. The cutting and heat sealing operation is also limited by the speed with which the apparatus can be reciprocated.